Several theories concerning the nature of visual processing and architectural function of the primary visual cortex have evolved from the basic understanding of the receptive field characteristics and how these receptive fields interact at different cortical levels. Current evidence indicates that in the adult primate and cat cortex, receptive field properties show a significant degree of integration occurring in the primary visual area (V1). The degree of receptive field modifiability and its neurological substrate, however, remain controversial. The goal of this project is to determine the role of the long range lateral connections in generating receptive field malleability after exposure to an artificial scotoma. The study will investigate three possible synaptic mechanisms by which intrinsic horizontal connections could modify the RF properties. Their effect may be due to an increase in synaptic efficacy, due to a general increase in excitability, or due to specific inhibitory and /or excitatory postsynaptic input. The experimental approach of this study incorporates the artificial scotoma electrophysical techniques. However, this proposal expands upon their methodology in two different ways: 1) Pharmacological manipulations will be used to explore the possible synaptic mechanisms. 2) Tetrodes will give a more complete picture of the scotoma's effects on the population of cortical neurons. These two modifications will help to obtain greater insight to the degree of RF malleability and the possible mechanisms generating these changes. Ultimately, this information will help to give a deeper understanding of how the primary visual cortex integrates information to form visual perception and imagery.